The present invention relates to a hydrogenated block copolymer having a specific structure; and to a resin composition which comprises an alloy of a polypropylene resin with a polyphenylene ether or polystyrene resin and the hydrogenated block copolymer having a specific structure, which composition is improved in the balance among appearance of the molded article; tensile elongation at break and moldability by the incorporation of the hydrogenated block copolymer, and which composition has characteristics of both the polypropylene resin and the polyphenylene ether resin or polystyrene resin in combination.
Polypropylene resins have been used in various fields as a molded article owing to their excellent organic solvent resistance and chemical resistance, however, they are accompanied with the drawbacks such as low rigidity and low heat resistance. Polyphenylene ether resins, on the other hand, are accompanied with such a problem as inferior organic solvent resistance in spite of having excellent rigidity and heat resistance. Polystyrene resins are inexpensive and excellent in moldability and rigidity, but inferior in organic solvent resistance. A mixture of these resins has been proposed as a resin composition having merits of each of the resins in combination. A polypropylene resin has only poor compatibility with each of a polyphenylene ether resin and a polystyrene resin so that systems further comprising a compatibilizing agent are proposed (JP-A-53-71158, JP-A-5-88960 or JP-A-59-100159 (The term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)). These systems are however accompanied with the problems that morphology tends to undergo a change upon heat retention or at the time when a solidifying rate is not uniform in a mold and flow marks appear depending on a change in the molding conditions or depending on the place of the molded article, which makes them unsuitable for practical use. In addition, the resin composition has recently been required to have high tensile elongation at break, among various mechanical properties such as rigidity and impact resistance, to prevent the molded article from being broken, when exposed to stress. As a compatibilizing agent exhibiting morphology stability, a diblock copolymer having segments compatible respectively with the resins to be blended are most effective. It is also known that the use of such a diblock copolymer, however, prevents exhibition of high tensile elongation at break, because the strength on the interface between the two resins becomes low. Thus, the external appearance of the molded article, which varies depending on the morphology stability upon thermal retention, and tensile elongation at break are physical properties which have been unable to be satisfied so far simultaneously. For the improvement of morphology stability upon heat retention, it is preferred that the segments of the block copolymer, which is added as a compatibilizing agent, compatible with the resins respectively each has a higher molecular weight. An increase in the molecular weight of the segment to impart it with a sufficient molecular weight lowers fluidity, leading to a deterioration in the moldability or prevents the exhibition of desired physical properties owing to poor dispersion.
The addition of a hydrogenated block copolymer as a compatibilizing agent is proposed, for example, in JP-A-63-225642. This publication discloses a resin composition comprising a polypropylene resin, a polyphenylene ether resin and a hydrogenated block copolymer, and examples using a styrene-hydrogenated butadiene diblock copolymer and a styrene-hydrogenated butadiene-styrene triblock copolymer as the hydrogenated block copolymer have been effected therein. Diblock, triblock and tetrablock structures are exemplified as preferred structures of the hydrogenated block copolymer. Concerning the tetrablock structure, however, neither description on the amount of the terminal hydrogenated butadiene block, which is specified particularly in the invention of the present application, nor suggestion about its effects is included in the above-described disclosure. Examples using the tetrablock structure are not also included therein. The external appearance of the molded article which depends on the morphology stability upon thermal retention and tensile elongation at break, which are problems to be solved by the present invention, are not satisfactory in accordance with the above-described conventional technique.
JP-A-9-12804 discloses a resin composition comprising a polypropylene resin, a polyphenylene ether resin and a hydrogenated block copolymer. Examples of a styrene-hydrogenated butadiene-styrene-hydrogenated butadiene block copolymer and a hydrogenated butadiene-styrene-hydrogenated butadiene-styrene-hydrogenated butadiene block copolymer used as the hydrogenated block copolymer have been effected therein. Although this publication includes a description that the composition is excellent in heat resistance, rigidity and tenacity (particularly, elongation), the moldability and external appearance of the molded article are not satisfactory. Moreover, it includes neither a description on the amount of the terminal hydrogenated butadiene block nor a suggestion about its effects.
JP-A-9-145238 discloses, as an inner wall material for refrigerator, a resin composition comprising a polypropylene resin, a polystyrene resin and a hydrogenated block copolymer. This publication includes neither a description of the amount of the terminal hydrogenated butadiene block in the hydrogenated block copolymer nor a suggestion about its effects. Moreover, it does not include examples effecting the same. According to this technique, external appearance of the molded article which depends on the morphology stability upon heat retention and tensile elongation at break, which are problems to be solved by the present invention, are not satisfactory.
An object of the present invention is to provide a resin composition excellent in rigidity, heat resistance and organic solvent resistance and also well-balanced among the appearance of the molded article, tensile elongation at break and moldability; and a hydrogenated block copolymer for obtaining the composition.
With a view to attaining the above-described objects, the present inventors have carried out an extensive investigation. As a result, it has been found that a resin composition comprising a hydrogenated block copolymer having a specific structure, a polypropylene resin, and a polyphenylene ether resin or polystyrene resin effectively attains the above-described objects, leading to the completion of the present invention.
The above-described objects of the present invention have been achieved by the following hydrogenated block copolymers and resin compositions.
A hydrogenated block copolymer which comprises at least two polymer blocks A each mainly comprising an aromatic vinyl hydrocarbon compound monomer unit and at least two hydrogenated polymer blocks B each mainly comprising a hydrogenated butadiene monomer unit, at least 90% of olefinically unsaturated double bonds in the polymer blocks mainly comprising a butadiene monomer unit before hydrogenation having been hydrogenated,
wherein at least one of the block at the terminal of the hydrogenated block copolymer is the polymer block B,
wherein the proportion of the terminal polymer blocks B in the hydrogenated block copolymer is at least 0.1 wt % but less than 9.1 wt %,
wherein the proportion of the aromatic vinyl hydrocarbon compound in the hydrogenated block copolymer is at least 25 wt % but less than 80 wt %, and
wherein the 1,2-bond content of the polymer blocks mainly comprising a butadiene monomer unit before hydrogenation is, on average, at least 60 mol % but less than 99 mol %.
2. The hydrogenated block copolymer according to the above embodiment 1, wherein the proportion of the aromatic vinyl hydrocarbon compound in the hydrogenated block copolymer is at least 25 wt % but less than 70 wt %.
3. The hydrogenated block copolymer according to the above embodiment 1, having a domain degradation temperature (Tdd) of 150xc2x0 C. or higher.
4. The hydrogenated block copolymer according to the above embodiment 1, wherein the proportion of the terminal polymer blocks B in the hydrogenated block copolymer exceeds 0.5 wt % but less than 5.0 wt %.
5. A resin composition comprising the following components (1), (2a) and (3):
(1) 20 to 80 parts by weight of a polypropylene resin,
(2a) 20 to 80 parts by weight of a polyphenylene ether resin, and
(3) 1 to 40 parts by weight of the hydrogenated block copolymer according to any one of the above embodiments 1 to 4.
6. A resin composition comprising the following components (1), (2b) and (3):
(1) 20 to 80 parts by weight of a polypropylene resin,
(2b) 20 to 80 parts by weight of a polystyrene resin, and
(3) 1 to 40 parts by weight of the hydrogenated block copolymer according to any one of the above embodiments 1 to 4.